Apparatus and method for adaptively interpolating a full color image utilizing luminance gradients

Abstract

Adaptive interpolation is performed by apparatus operating upon a digitized image signal obtained from an image sensor having color photosites that generate a plurality of color values, but only one color per photosite. A digital processor obtains gradient values from the differences between luminance values in vertical and horizontal image directions. The gradient values are compared to a programmable threshold in order to select one of the directions as the preferred orientation for the interpolation of additional luminance values. The interpolation is then performed upon values selected to agree with the preferred orientation.

What is claimed is: 
     
       1. Apparatus for processing a digitized image signal obtained from an image sensor having color photosites that generate a plurality of color values, but only one color value for each photosite location, said apparatus comprising: means for storing the digitized image signal as a pattern of luminance and chrominance values, wherein some photosite locations lack luminance values;   a processor operative with said storing means for generating an additional luminance value missing from a photosite location by the interpolation of the additional luminance value for such locations from luminance values at nearby photosite locations, said processor including means for generating gradient values from the differences between luminance values in at least two image directions;   means for comparing the gradient values to one or more thresholds;   means responsive to the threshold comparison for selecting one of said at least two image directions as a preferred orientation for the interpolation of the additional luminance value; and   means for interpolating the additional luminance value from luminance values selected to agree with the preferred orientation.     
     
     
       2. Apparatus as claimed in claim 1 wherein said one or more thresholds are adjustable. 
     
     
       3. Apparatus as claimed in claim 1 wherein said at least two image directions are horizontal and vertical directions. 
     
     
       4. Apparatus as claimed in claim 1 wherein said pattern of luminance and chrominance comprises chrominance values interspersed in a checkerboard pattern of luminance values. 
     
     
       5. Apparatus as claimed in claim 4 wherein said luminance color is green, and said chrominance colors are red and blue. 
     
     
       6. A method for interpolating missing luminance values from a digitized image signal obtained from a color image sensor having photosites that generate a pattern of actual luminance and chrominance values, one actual value for each photosite location, said method comprising the steps of: obtaining gradient values from the differences between actual luminance values in vertical and horizontal image directions;   comparing the gradient values to a predetermined threshold;   selecting the image direction, in which the comparing step indicates scene structure, for the interpolation of the missing luminance values; and   interpolating each missing luminance value from actual luminance values at nearby locations corresponding with the selected direction, and thereby with the scene structure.   
     
     
       7. Apparatus as claimed in claim 4 wherein the gradient values are developed from luminance values from photosites immediately adjacent the photosite for which said additional luminance value is interpolated. 
     
     
       8. A method as claimed in claim 6 wherein the gradient values are developed from luminance values from photosites immediately adjacent the photosite for which said additional luminance value is interpolated.